Core Lab Only: The specific aims of the proposed study are to determine the accuracy and variability of the renal clearance of 125I-iothalamate, and TC-DTPA, after subcutaneous bolus administration in type I diabetics. We propose to compare, 20 subjects, in two measurements performed one month apart, simultaneous renal clearances of inulin during a continuous intravenous infusion (the "gold standard"), meglumine (non-radioactive) iothalamate during a continuous intravenous infusion.